Gas adsorption



A. H- SCHUTTE GAS AD SORPTION Dec. 27, 1-949 Filed Feb. 24, 1945 ATTORNEY Patented Dec. 27,1949

UNITED PATENT F GAS ABSORPTION August Henry Schutte, Hastings on Hudson, N Y., assignor to The Lummus Company, New York, N. Y., a corporation of Delaware Application February 24, 1945, Serial No. 579,636

17 Claims.

This invention relates to improvements in the artv of separating a gas from a mixture Of gase by contact of the mixture with a solid adsorbent material in a divided state. More particularly, the invention relates to improvements in an adsorption system wherein contact is effected between the gaseous mixture and the adsorbent for selective adsorption of a gas of the mixture and wherein the adsorbent is subsequentl heated to efiect desorption of said gas and then cooled to an optimum temperature for performance of the adsorption step and reemployed in said step.

It is customary in such a system to heat and. cool the adsorbent in an inefiicient and costly manner by indirect heat exchange. An adsorp-v tion system of large capacity requires many thousands of square feet of heat exchange surface entailing great cost of plant equipment, much servicing and often suspension of plant operation during servicing. Moreover, indirect heat ex, change is especially inefficient in such. a system because of the fact that heat exchange must occur largely by condition between the solid. adsorbent and the temperature-conditioning fluid. Consequently, excessive area of heat exchange surface is required.

An important object of the present invention is to provide for more efiicient performance of said heating and cooling and obtain substantial economy in plant equipment and in cost-of opera tion and maintenance.

Another object of the invention is to provide;

for satisfactory performance of the heating and 1 cooling by direct heat exchange.

Other objects and advantages of the invention will be apparent from the following descriptionthereof taken in connection with the accompanying drawing which is a diagrammatic illustration of a preferred form or embodiment of the invention in a continuous gas adsorption system employing a finely divided or powdered solid ad.- sorbent material.

It is to be understood that this improvedsystem is applicable to the separationv by adsorption. of any desired gaseous component. of a mixture of gases and that in the following specification and Claims the term gases is meant to include vapors.

This application is a continuation-in-part of my similarly-entitled copending application, Se

re ui e s. 'ductio 2. r d component therefrom. the aseous prod: o e from. cracking. for o ta nin s at. ere czn o cores. common ntsush as t:.. na rcpr ena etc;

ccordin t presen int ntion the adsorb: t ma erial s p sed oi usts nsuccession hrou h an adsor ion. zone scrption zone-a. cooling zo e and, be to t ev adsor i hin. t adsorpt Zone the torrent iss e m ledt cont m ts sha es s ream Qt the a e t e s parat d- W .1 the desorpt on, ne the dsorb t be ring e adsexberlomm: n w; ofthe ha s mir h; 15 direct y hea ed to in 1 il t QP QFRQQQ by 1 ho van at has e or i n c vapor s nd nsed 1 12 .nli fi ads nt amit e. t er. s e e cond nsate ot th por. i passed to the cooling zone A 19W pre sure C9111 ,dition m n aine W m he lihe cne to a s e o ti n of; said ond sate and th mby effect dir t ol ng of. the adsorbent to a temperature suitabl for reemployn ent thereof Within h d Qr -t on zone- .In t e cours of passage thereof from; zone to zone, the adsorb But i q ain d to orm a sravity packed Seal: ns, a s he o between each zon an the: mediately following zon and thereb ainta n required p sure ffierent. s between he zones" Provision is also made for em entrecove'ry ofad, sorbent entrain d y the ases on a sed from the adsorption zone and the desorpti also for recovery of any fixed gas evacuated from the coolin zone along with the vaporized e a...

v densate.

continuously introduced into. the system z I a l nev l whi h discharsies throu h an injection nozzle 2, into one end of. an elongatfidlchfimbfiif 3.

vdefining n adsorption zone. The finely divided. "adsorbentisuch as powdered charcoal or silica gel,

.t o h i o e. he adsorbe tbe omes dis e rial No. 504,2'75, filed September 29, .1943, now

" uted' through the charge for maximum adsorption contact therewith. Desirably, a pressure of, app o mately 5 lbs. gauge: and a mperature of not over F. are maintained within the ads sorption ne. Th o ta t chamber discharges into a separator 4 of-the well-.linown .cyclone type. In effect, this separator 1? ns av continufie tion of the d rpt on, or ontact. zenesinee contact continues r u hout a portion. the travel e eeu medium th ugh sep rators Within the latter the adsorbent, bearing the ad.-

9: v ne and In the ope ation of the system, he charge i 3 sorbed gas, is centrifugally separated from the gaseous medium and falls to the bottom of the separator casing, while the lean gaseous medium is passed from the top of the separator through the line 5.

At its bottom the separator 4 opens into a vertical conduit 6 which receives the separated adsorbent and constrains it to form a gravitypacked column. The packed mass of adsorbent so formed serves as a seal to prevent exchange of gas between the adsorption zone and a following desorption zone and maintain a required pressure differential between said zones. In order to maintain a sufiicient depth of the adsorbent for sealing efiect, the conduit 6 is provided with a damper or butterfly valve I to control discharge of the adsorbent from the conduit. Through a connection 3 of any well-known type, the valve is operated in response to variations in the level of the accumulated adsorbent at the bottom of the separator. A cyclone separator 9 forms a chamber defining the desorption zone, and a lateral screw conveyor It delivers the used adsorbent from the lower end of the tube 6 to said zone. The screw of the conveyor is power-driven through a pulley at the outer end thereof.

Adsorbent delivered 'by the conveyor I is heated by direct heat exchange with a hot vapor to efiect desorption. For that purpose a hot vapor such as steam, for example, is introduced into the conveyor and into separator 9, through lines II and I2, line I2 being provided with a conventional flow control valve I3. The heat provided by the steam so supplied causes desorption of the gas from the adsorbent and at least a portion of the steam is condensed upon the adsorbent. Within the separator 9 the release gas and the delivered adsorbent are whirled to separate the latter which falls to the bottom of the separator casing while the gas escapes through the overhead line I4. Desirably a pressure of approximately 7 to 10 lbs. gauge, and a temperature of approximately 230 F. are maintained within the desorption zone. such pressure is maintained by a pressure-controlled valve I in the line I4, and the temperature is maintained through control of steam admission by the flow control valve I3 in the steam line I I. In order to control the degree of saturation and to improve the selectivity of the adsorbent within the adsorption zone a controlled amount of the desorbed gas is returned to said zone for readsorption. For that purpose, a branch line H leads from the line I4 to the separator 4 and is provided with a flow control valve A seal-forming means similar to that previously described herein is provided at the lower end of the separator 9. This means includes a vertical adsorbent within the desorption zone is evaporated and cooling of the adsorbent is effected, preferably to a temperature of from to 80 F. If desired, further purging of the adsorbent within the cooling zone may be performed by admission of a controlled amount of gas from the line 5 through a line 23 to said zone. The line 23 is provided with a flow control valve 24. If it is found that the amount of condensate deposited upon the adsorbent within the desorption zone is insufiicient to effect adequate cooling by evaporation within the cooling zone, distilled water in controlled amount may be delivered through a line 25 to the steam supply line II. Line 25 is provided with a flow control valve 26.

A seal-forming means similar in general to those previously described herein is provided at the lower end of the cooling chamber. This means includes a vertical conduit 6b to receive the cooled adsorbent. A rotary star valve 28 is substituted for the damper of the previously described seals and is continuously operated at a constant rate by a motor M. At its lower end the conduit is in delivery connection with the adsorption zone at approximately the point of injection of the gaseous charge from the line I. Owing to the fact that maintenance of a relatively high pressure differential between the adsorption zone and the cooling zone is required and owing also to the fact that the higher pressure is at the lower end of the column of adsorbent within the conduit 8b, the latter is made relatively long to contain a column say, feet high. A column of such height will make an adequate seal and prevent passage of charge gas upwardly to the cooling zone. An indicating device 817 is connected to the lower portion of the casing of the separator I9 to indicate the level of the adsorbent accumulated within the conduit 61) and the casing. When said level falls, additional adsorbent is supplied to the system, as will be explained hereinafter.

Provision is made for recovering adsorbent discharged from the separators 4 and 9 and also for recovering gas evacuated from the cooling zone. Gas'discharge line 5, from the separator 4, delivers to the lower portion of a scrubbing unit 29 provided with internal baflles 3! A suitable liquid such as water, for example, is introduced into the upper portion of the scrubber through the line 3!. The gas flows upwardly counter to the descending water and is scrubbed thereby and discharged through the line 32. The latter has a pressure control valve 33. This valve is set to maintain the required pressure within the adsorption zone, the line 32 being connected to said conduit ta to receive the separated adsorbent, a

butterfly valve Ia and a control connection Go for operating the valve in response to variations in the level of the adsorbent at the lower end of the separator 9, to maintain a depth of the adsorbent sufficient to maintain the required pressure differential between the desorption zone and a following cooling zone.

A cyclone separator I9 forms a chamber defining the cooling zone, and a screw conveyor IOa, similar to conveyor I0, continuously delivers the adsorbent from the column 6a to the cooling zone. Through a line 26 provided with a steam jet ejector 2|, discharging into a surface condenser 22, an absolute pressure of approximately 25 to 30 mm. is maintained within the cooling zone. Thereby the steam condensate deposited upon the sate is discharged through a valved bottom line 39 from said tank.

The used scrubbing water collecting at the bottom of the scrubbers and containing recovered adsorbent is discharged through lines 40 and M,

' subject to operation of float-controlled valves 42 and $3 in said lines respectively, and thence to a line 44 which delivers the water to a circulating tank 45. Water is passed through a bottom line 46 from said tank to a pump 41 which delivers aseaeqi 6: e w r o a e r a l rifi r 4 Mesa: sqt tiea zeta. is; fitdgliia "9 t r' et v r i eiis ib tit 4 W 19. d si 'e nth c a ifi into fi r t ii hsl m ssed aft w 'l fi latter In'ay 'be ofany suitable 2yP $lih a tion zQne to a des a J afiencllos'edchain conveyor, for example. The 5 20,1; m succgssion theimproicernent'inc di i ffi iv r h slud v a ch te u e .9. si h -#1 int qd tilis i flt pdrtf h We ha es h u g i o the conveyor "it. withinl e cl qrnti n zone; to, erte t deso tion lead-mg the cooling o u h a in e la fle qa de osi Qt a. Q densate QI th t n e ad rbe t, es abl sh n a low pressure;

li' aid'bhut e ii sme ad b beht' ex i n wit n aid. cool n zon o e ect. wan-1- be suppliedt o the s ystei r1 When the necessity ifoif 10 c N w I I firi is d c t y e vel, i d atq v 0 r, Q sa cqnd nnsate an onseq t 921.:- wissbbietd with. he epata qt L9, Qlai iesi- 35. Q the. ads rbent nd o t nuously ga s ng;- wtri'sdishafgd bythe clarifier 45: through thje' eoql edfid orbenfi icqm the-{cooling zone tothe; 1155186 hit/inst ranc 5:1- ead ng. o, he. sue. es rnti nz na tioi'i-s'ide of'a'f pump 5-2. Said pump deliversthe V 2 In an, adsorption process; wherein contactfis, wqteflb the tank 45; through a line. 53-. when effiec d betweer a'gaseous mixtu eand asolid ad desired; Water'may be discharged f r a we the ysrl qt ie i in. a divi ed tate wit inn. ad qrp e ii' t0fifr611in61intsby ope ti Qt altal h one. mr adsor tion f; a. mmn nt of atin fljpbfieit fi i y y ild h q ime tiaol W and whe i the? a s b nt is ha -s q aiter the h a ic ater. ma. e 42 con a ts ro theadso i n zo oads supplied through a valved line 55 connected; to sorption zoneanda coolingzo rfigeinsuocession tli e the line 53 leading to the tank 45. 'A l ine 55 con; in; oyement including thesteps oi -introducing; a, ducts water from th tank 45 to apurnp SI'Which hot v apor to the adsorbent withinth desorption delivers the water through a line 58 to, thg line zone to, effect, desorption cause depositof a 3ili'w'h'ich supplies Water to the scrubbers 29" and condensate oi the vapor, upon the. adsorbent 34A 1' Line 58 is provided with a flow-control valve pas ing the adsorbent from the desorption 9 1?: 5a; V to cooling zone and establishingalow,pness%e ndu s h scr b s i qm. the ondi ion. within s d 90 1 15;zcna eefieqteveee suction tank-38 to the suct on s de of a compres oration oi said, condensate and consequent cook. son 61 and the latter forces; the gas into a coningpithe adsorbent. me tg 5 32 g ide at 3 1. 3-

an ad orp m ocess w rein on rac e: m w a mm .c 9 tes d e w esepus; mix ur and a d! e; nd a i s a a de d and: dserhent a d te, w th niana s rm; product,- through a hne 65; subiect to operation zon e for adsorption oi a component of; said mix OfJ afloat -conigolled- 56 mfsaidlt lriie, 1311 5 wherem the adsgrhegfi i ass ed af 1;; Gaseous me q wn IQ Q m g such contact from the adsorptlon zone to a e 10316 throughh a d: the FQ I s qmtipnize i nd: a o lips; ma n; su cess me as condensateand from the condensenZZ through a lineG-I-to a tanl; 58; mg a h ot vapor to theadsorbfint, w thin the def f} 5 the a g qe, 9m 4Q soljption zone to ef fectdesorption;and cause 1. an .v t 0 e me o -a pump a aif' uma positof. a- .condensate.of, the vapor upon the ad-r deliveredh condensate, whichis mainly water ibnt; establishing a low. pressure conditi throughal ne H to thewater h ne 4fl'lead ng frorn within; safid cooling. zone, t musev e'vaporafioni t; the scrubbersto thetank; Dellvely i said condensate and. consequent cooling; o f the through the line H is controlledby a float cor 5 aq rbent passing the cooledadsorbent f rornthe trolled valve'l zr Uncondensed gas ispassedfrom cqgl lpg zone to the. adsorption zone and; con;-v

n l a 9 69 PQ 0 9 ne Q mz sf yi b .7 n 0 gas be .ween he zones,-

drawn. from the. etcondenserthrough a line 1-7 41 In: anaadsorptipn pmplessa herein contacpis haying ablow-er .18; and leadmgto the chargelmg effegteq betwegn v a galspequs mixture a? 501m, :1.

1 4 zone, for adsqrptionof a component of said mix;-

gf ite f g p i g 'i. 5 ture; and wherein theadsorbent is.- heated after a ain? 0 h f iffi g 5 *suoh 0mg: Q fieQtdesorption and issubse-r.

a n 1 3 provemen=z inc uding; the steps ofpassing byrdirect meatexchange.v Therebygreat econom-- E Zone if" desorpgmihzone and: h is obtaineddn cost. of plant equipment, mainteg gg ggg; 2 z f g i fid z g gb nanee heatinput andcirculationoftemperaturep p 0 cor iditioninglfiuid. It willvbe. seen also thattthel densate of the vaporupon the adsorbept passinuentionnprovidesihighly efiicient recovery fea-. 1 3 'f g fit desirptmn Z0138" tureslforicoonerationwith the direct thermal mg'zonei es a 15 mg Ow preSsm-e conditioning featur sr It is of. course, to be understood thatztheabove-i. description is merely illustrative and in nohwisei limitingandthatl intend to, comprehend. within this, innentimsuch modificationsasrare included h scone o the followin la ms coolihgrof the adsorbent; passinggaseous, media, from the v adsorption zoneand the desorption zpne and scrubbing them separately with a liquid; recovering sludge from the vused scrubbing Y uid) @nd'n n i n ludee otheiad orbl continuous adsorption.processhwhereim P 1 ii'omth dso ionzone ,tcthede orn ion, j j e' edt'wiii@fgasoiisfifiii ne, ecir ulatin h i ids. re d? rom. aid a adsorb miaditided niad L. fl i l fifiiri fiidi gt iuh in fi s ndfinfiinfila 'conditionwithin' said cooling zoneto efiect" evaporation of -said condensate and consequent;

5. In an adsorption process wherein contact is,

effected between a gaseous mixture and a solid adsorbent in a divided state within an adsorption zone for adsorption of a component of said mixture, and wherein the adsorbent is heated after such contact to efiect desorption and is subsequently cooled and reemployed for contact, the improvement including the steps of passing the adsorbent, after-such contact within the ad sorption zone, to a desorption zone and there introducing a hot vapor to the adsorbent to eiiect desorption and'cause deposit of a condensate of the vapor upon the adsorbent, passing the adsorbent from the desorption zone to a cooling zone, establishing a low pressure condition within said'cooling zone to effect evaporation of said,

condensate and consequent cooling of the absorbent, passing gaseous media from the adsorption zone and the desorption zone and scrubbing them separately with a liquid, recovering sludge from'the used scrubbing liquid and passing said sludge to the adsorbent passed from the adsorp-] tion zone to the desorption zone, recirculating the liquid freed from said sludge for reuse in saidscrubbings, condensing a portion of the gaseous medium received from the desorption zone and so scrubbed, and passing an uncon-' densible portion of such medium to the adsorp-' tion zone.

6. The improved steps for a gas adsorption process of the type wherein a solid adsorbent in a divided state is passed through an adsorption zone, a desorption zone and a cooling zone in succession, said steps comprising supplying heat to desorb-the adsorbed gas by introducing to the desorption zone a hot vapor, forming a suspension of the adsorbent within the desorbed gas,

controlling the temperature and pressure within the desorption zone to obtain a substantial deposit of condensate of the vapor upon the ad- 7,

sorbent, separating the suspended adsorbent from the gas, creating a reduced pressure within the cooling zone and thereby cooling the ad.- sorbent for reuse by evaporating liquid deposit thereon and forming a suspension of the adsorbent in the resulting vapor, and separating the suspended adsorbent from said vapor.

7. The improved steps for a gas adsorption processof the type wherein a solid adsorbent in a divided state is passed through an adsorption zone, a desorption zone and a cooling zone in succession, said steps comprisingsupplying heat to desorb the adsorbed gas by introducing to the desorption zone a hot vapor, forming a suspension of the adsorbent within the desorbed gas and a deposit of condensate of the vapor upon the adsorbent, separating the suspended adsorbent from the gas, supplementing said deposit by introduction of liquid in controlled amount to the desorption zone, creating a reduced pressure within the cooling zone and thereby cooling the adsorbent for reuse by evaporating liquid deposit thereon and forming a suspension of the adsorbent in the resulting vapor, and separating the suspended adsorbent from said vapor..

8. The improved steps for a gas adsorption process of the type wherein a solid adsorbent in a divided state is continuously passed through an adsorption zone, a desorption zone and a cooling zone in succession and back to the adsorption zone wherein contact is effected between a gaseous mixture and the adsorbent for adsorptionof a component of the mixture, said steps coniprising supplying heat to desorb the adsorbed gas by introducing to the desorption zone a hot vapor, forming a suspension of the adsorbent within the desorbed gas and a deposit of condensate of the vapor upon the adsorbent, separating the suspended adsorbent from the gas, supplementing said deposit by introduction of liquid in controlled amount to the desorption zone, maintaining a reduced pressure within the cooling zone,

and thereby cooling the adsorbent by evaporating liquid deposit thereon and forming a suspension; of the adsorbent in the resulting vapor, separating the suspended adsorbent from said vapor, and y introducing to the cooling zone a controlled" amount of an unadsorbed component of the,

gaseous mixture from the adsorption zone to thereby control the degree of evaporation of said liquid deposit. 7 9. The improved steps for a gas adsorption process of the type wherein a solid adsorbent in a divided state is passed through an adsorption" zone, a desorption zone and a cooling zone in.

succession and back to the adsorption zone wherein contact is effected between a gaseousv mixture and the adsorbent for adsorption of a component of the mixture, said steps comprising supplying heat to desorb the adsorbed gas by introducing to the desorption zone a hot vapor,

forming a suspension of the adsorbent within the desorbed gas and a deposit of condensate of the vapor upon the adsorbent, separating the suspended adsorbent from the gas, creating a re- 1 duced pressure within the cooling zone and thereby cooling: the adsorbent for reuse by evaporating liquid deposit thereon and forming-.

a suspension of the adsorbent in the resulting vapor, separating the suspended adsorbent from said vapor, and introducing to the cooling zone a controlled amount of an unadsorbed component of the gaseous mixture from the adsorption zone to thereby control the degree of evaporation of said liquid deposit.

10. The steps for a gas adsorption process claimed in claim 6 with the additional steps of passing the cooled adsorbent from the cooling zone back to the adsorption zone, and constrain-. ing the adsorbent, in each passage thereof from zone to zone, to form a gravity-packed sealing mass thereof preventing exchange of gas between thezones.

11. The improved steps for a gas adsorption process of the type wherein a solid adsorbent in a divided state is passed through an adsorption zone, a desorption zone and a cooling zone in succession, said steps comprising supplying heat to desorb the adsorbed gas by introducing to the desorption zone a hot vapor, forming a deposit of condensate of said vapor upon the adsorbent, supplementing said deposit by introduction of liquid in controlled amount to the desorption I chamber, and creating a reduced pressure within the coolingzone and thereby cooling the adsorbent for reuse by evaporation of liquid deposit thereon.

12. In an adsorption process wherein contact is effected between a gaseous mixture and asolid adsorbent in a divided state within an adsorption zone, for adsorption of a componentof said mixture, and wherein the adsorbent is heated after such contact to efiect desorption and is subsequently cooled and reemployed for contact, the improvement including the steps of passing the adsorbent, after such contact within the adsorption zone, to a desorption zone and there introducing a hot vapor to the adsorbent to effect desorption and cause deposit of a condensate of the vapor upon the adsorbent, passing the adsorbent from the desorption zone to a cooling zone, establishing a low pressure condition within said cooling zone to effect evaporation of said condensate and consequent cooling of the adsorbent, passing gaseous media from the adsorption zone and the desorption zone and scrubbing them separately with a liquid, recovering sludge from the used scrubbing liquid and passin said sludge to the adsorbent passed from the adsorption zone to the desorption zone, condensing a portion of the gaseous medium received from the desorption zone and so scrubbed, and passing an uncondensible portion of said medium to the adsorption zone.

13. In an adsorption process wherein contact is eflected between a gaseous mixture and a solid adsorbent in a divided state within an adsorption zone, for adsorption of a component of said mixture, and wherein the adsorbent is heated after such Contact to eflect desorption and is subsequently cooled and reemployed for contact, the improvement including the steps of passing the adsorbent, after such contact within the adsorption zone, to a desorption zone and there introducing a hot vapor to the adsorbent to effect desorption and cause deposit of a condensate of the vapor upon the adsorbent, passing the adsorbent from the desorption zone to a cooling zone, establishing a low pressure condition within said cooling zone to effect evaporation of said condensate and consequent cooling of the adsorbent, passing a minor portion of an unadsorbed component of said mixture from the adsorption to the cooling zone, passing a major portion of said unadsorbed component from the adsorption zone and scrubbing it with a liquid, passing gaseous media from the desorption zone and separately scrubbing it with a liquid-recovering sludge from the used scrubbing liquid from said two scrubbing steps and passing said sludge to the adsorbent passed from the adsorption zone to the desorption zone, condensing a portion of the gaseous medium received from the desorption zone and so scrubbed, and passing an uncondensible portion of said medium to the adsorption zone.

14. Apparatus for an adsorption system of the type wherein a solid adsorbent in a divided state is passed through an adsorption zone, a desorption zone and a cooling zone in succession, said apparatus including a desorption chamber having an adsorbent delivery conduit portion in receiving connection with the adsorption zone, and a portion opening into said conduit portion to receive the adsorbent for separation thereof from desorbed gas and having an outlet conduit fo the gas and an outlet for the adsorbent; means for deliverin hot vapor to said conduit portion at a point materially spaced from the connection of said conduit portion with said separating portion of the chamber; valve means to control discharge of gas through said gas outlet conduit and retain a predetermined pressure in the desorption chamber; a cooling chamber also having an adsorbent delivery conduit portion in receiving connection with said desorption chamber and a portion opening into the conduit portion to receive the adsorbent for separation thereof from vapor and having an outlet conduit for the vapor and an outlet for the adsorbent; and suction means connected to said vapor outlet conduit to create low pressure in the cooling chamber.

15. The apparatus claimed in claim 14, and including means to deliver a liquid into the said separating portion of the desorption chamber.

16. The apparatus claimed in claim 14, and including upstanding adsorbent delivery conduits arranged respectively to deliver the adsorbent from the adsorption zone to the desorption chamber, from the latter to the cooling chamber and from the cooling chamber back to the adsorption zone, and means to control passage of the adsorbent through each of said conduits to maintain therein a gravity-packed sealing column of the adsorbent.

17. The apparatus claimed in claim 14, and including means for delivering a controlled amount of unadsorbed gas from the adsorption zone to the cooling chamber.

AUGUST HENRY SCHUTTE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,577,534 Miller Mar. 23, 1926 1,616,547 Pontoppidan Feb. 8, 1927 1,758,398 Hasche May 14, 1930 1,836,301 Bechthold Dec. 15, 1931 2,009,569 Wallis July 30, 1935 2,247,594 Bayerl July 1, 1941 2,270,903 Rudbach Jan. 27, 1942 2,340,398 MacMullin Feb. 1, 1944 2,397,566 Schutte Apr. 2, 1946 

